Spun-bond nonwoven fabric is a fabric generally produced from filaments or fibers of plastic material, e.g. polypropylene, formed by spinnerets by a filament-drawing process or by a melt-blown process whereby the strands of the thermoplastic emerging from the spinneret are broken into fibers, disposed upon a foraminous surface against which the fibers or filaments may be drawn by suction, or otherwise transformed into a fleece of nonwoven filaments or fibers which can be bonded together.
In general, these techniques require that the thermoplastifier synthetic resin or plastic material, i.e. the thermoplastic material which is subjected to shear and like action in an extruder and liquefied under heat and pressure is fed to a distributor which, in turn, distributes the molten thermoplastic material to a spinning beam or unit from which strands of the thermoplastic material can emerge and can be contacted with an air stream.
Depending upon the nature of such contact and the type of air stream used, the processes can produce discrete filaments from individual spinnerets which are substantially endless, can pass through a drawing nozzle and can be deposited in random loops upon the foraminous collecting surface, e.g. perforated belt or the like. This process is generally referred to as a spun-bond process.
It is known to break the strand of thermoplastic material emerging from each spinneret into discrete fibers which can be similarly or differently collected in a nonwoven fleece utilizing the so-called melt-blown process.
In, for example, German patent DE-OS 25 32 900 and the publication entitled "Melt-blown Information Reifenhauser", of 18 May 1989 and disseminated by the assignee of this application, a process is described whereby the individual spinnerets of the spinning unit are fine bores with a diameter generally less than 1 mm, for example, a diameter of 0.5 mm, and a spacing in rows and columns of about 1 mm. The fabrication of such spinning units is a highly expensive matter and this type of spinning unit has a limited throughput. The individual plastic fibers or filaments have a relatively smooth surface whether the process involves filament production or the melt-blown process for producing fibers. In both cases as well, the surfaces of the plastic fibers or filaments influence the quality of the finished spun-bond nonwoven.